The NIH Animal Genetic Resource (NIHAGR) maintains many unique rat genotypes used as models of normal and disease processes in man. Effective management of this resource would be facilitated by the development of embryo cryopreservation procedures for long-term banking. In order to develop banks of cryopreserved germ plasm from laboratory rats, protocols for each step of the embryo banking and rederivation process must be established. These would include the preparation and mating of embryo donor females, embryo collection, cryopreservation, thawing, and embryo transfer. Previous studies suggest that superovulation procedures developed for laboratory mice are not as effective when applied to laboratory rats. The principal objective of this project is to evaluate treatment with an analog of gonadotropin releasing hormone (GnRH-a) as an alternative approach to synchronize estrus cycles for embryo collection and cryopreservation.